The present invention relates to a communication system with a limited communication area.
In a communication system used in a field, for example, for communication in a hall, for simultaneous interpretation in an international conference, or for an explanation to visitors in a zoological garden or museum, a radiowave or induction communication system is used for the communication of information in such a limited receiving field. In this case, such a communication is often required to be limited within a specific area for the reason that the contents of the communication must be kept secret or that a fee-charging system is employed. The attempt to limit the communication area becomes difficult when the communication area is wide, even if an electromagnetic shielding method is employed for the purpose of limiting the communication area. In this respect, the communication system has many problems in practical use.
Particularly, to provide an explanation to visitors in a zoological garden or museum, a communication system is desired that has transmitters having a plurality of frequencies, which are substantially the same, which are used as carrier waves for transmitting communication signals having different information in different communication areas, and that has a receiver for receiving the different communication signals as the receiver is moved, without the necessity of a troublesome tuning operation. In such an application, there is no problem of interference when the adjacent communication areas are far away from each other. In the other case where the adjacent communication areas are close to each other, however, it is possible that the explanation in one communication area is received in another communication area or that the interference occurs.